1. Field of the invention.
The subject invention relates to pressure transducers and to methods and apparatus for handling a compatible solution relative to the circulatory system of a living organism with the aid of a catheter.
2. Disclosure statement.
The following disclosure statement is made pursuant to the duty of disclosure imposed by law and formulated in 37 CFR 1.56(a). No representation is hereby made that information thus disclosed in fact constitutes prior art, inasmuch as 37 CFR 1.56(a) relies on a materiality concept which depends on uncertain and inevitably subjective elements of substantial likelihood and reasonableness, and inasmuch as a growing attitude appears to require citation of material which might lead to a discovery of pertinent material though not necessarily being of itself pertinent. Also, the following comments contain conclusions and observations which have only been drawn or become apparent after conception of the subject invention or which contrast the subject invention or its merits against the background of developments which may be subsequent in time or priority.
The design and operation of equipment for handling a compatible solution relative to the circulatory system of a living organism shares with the design and operation of liquid pressure transducing devices a concern over the removal of air bubbles from the compatible solution or other liquid. Reference may, in this respect, be had to pages 202 et seq. of HEALTH DEVICES (July, 1979) published by the Emergency Care Institute, of Plymouth Meeting, PA 19462. As that publication cautions, "Even the smallest air bubble can cause significant waveform distortion and result in incorrect systolic and diastolic values. Make sure all air bubbles are flushed from the catheter, tubing, stopcocks, and especially the transducer dome chamber."
In general, the compressible nature of air bubbles diminishes and otherwise degrades a pressure transducer signal, while injurious or fatal effects may result from an injection of air bubbles into living organisms.
Yet, because of surface tension and other effects, air bubbles at the boundaries of liquid-receiving cavities, tend to resist externally induced attempts at their removal.
In this respect and with regard to present and potential areas of utility of the subject invention, reference may, for instance, be had to U.S. Pat. No. 3,157,201, by D. Littmann, issued Nov. 17, 1964, for a fluid exchange valve between a glucose or saline solution reservoir, a catheter and a transducer, U.S. Pat. No. 3,351,105, by M. S. Di Perna, issued Nov. 7, 1967 for a rechargeable dispenser including a ball valve, U.S. Pat. No. 3,565,056, by L. D. Statham, issued Feb. 23, 1971, for a body fluid pressure measuring device connected to a saline solution supply and to a needle or catheter, U.S. Pat. No. 3,631,850, by J. E. Levasseur, issued Jan. 4, 1972, for a pressure transducer apparatus for microhemocirculation studies, including a pressure dome formed of a flat base having a diaphragm portion and sidewalls that converge into a central opening coupled to a microcannula, U.S. Pat. No. 3,730,186, by L. H. Edmunds et al., issued May 1, 1973, for an adjustable implantable artery-constricting device, U.S. Pat. No. 3,731,680, by F. A. Wright, issued May 8, 1973, for a pressure monitor and control device particularly useful in a method for effecting extra-corporeal hemodialysis, U.S. Pat. No. 3,807,142, by S. R. Rich, issued Apr. 30, 1974, for high efficiency removal of gases and particles from paper pulp suspensions and other fluids, employing vortical separation stages, U.S. Pat. No. 3,811,429, by J. C. Fletcher et al., for an arterial pulse wave pressure transducer having a flexible membrane adjacent a fluid-filled cavity adapted to be placed on the skin over an artery, U.S. Pat. No. 3,865,100, by H. Kanai et al., issued Feb. 11, 1975 for apparatus for measuring blood pressure, including a dumbbell-shaped damping device, U.S. Pat. No. 3,942,564, by T. Nakazato, issued Mar. 9, 1976, for a fuel tank filling inlet port device designed for selective acceptance of different diameter filling nozzles, U.S. Pat. No. 3,996,027, by W. J. Schnell et al., issued Dec. 7, 1976, for a swirling flow bubble trap in which liquid is passed for swirling flow within a chamber for a migration of gas bubbles from an inner wall towards the center of the swirling flow, and U.S. Pat. No. 4,063,555, by B. Ulinder, issued Dec. 20, 1977, for a cannula assembly designed for administration of fluids from two separate sources of supply, and including a check valve associated with one fluid inlet.
Reference may in this respect also be had to U.S. Pat. 3,623,479, by C. C. Day, issued Nov. 30, 1971, for ECG electrode having a partition for preventing hydrostatic locks through intrusion of skin into the dome-shaped electrode. According to an embodiment disclosed in that patent, the partition may be segmented to provide separate spaced contact areas with the skin to better restrain the skin from intruding the cavity and for directing the flow of an electrically conductive paste from an entrance hole, and the expurgation of entrapped air throughout the cavity to exit holes. Such partition segments have sharp corners to reduce flow resistance to the entrapped air and conductive paste and supposedly to better guide their flow. In practice, however, the latter proposal is pretty much restricted to its disclosed form of utility, since the curved partition segmentation in question compartmentalizes the available conductive paste flow into a plurality of parallel branches, thereby substantially reducing the attainable momentum with which air bubbles could be swept from cavity boundaries.
An attractive solution to the problem under consideration is apparent from U.S. Pat. No. 4,063,553, by H. Karsh, issued Dec. 20, 1977, to the subject assignee. According to the methods and apparatus disclosed in the latter patent, a compatible solution is injected into a circular liquid-receiving cavity in a whirl which sweeps all regions of the circular cavity, thereby vigorously removing gas bubbles therefrom.
The embodiment shown by way of example in the latter patent employs an inlet tube for injecting the compatible solution at a predetermined location in a direction extending at an angle to a diametrical plane through the circular cavity and that predetermined location. The particular inlet tube is thus laterally offset from the catheter tube on the transducer dome.
In practice, this complicates the manufacture of the transducer dome structure relative to an arrangement in which both tubes would extend in the same diametrical plane. Of course, this does not derogate from the utility of the latter solution, but it does render its implimentation potentially expensive and in need of special manufacturing steps.
For completeness' sake, reference may also be had to my U.S. Pat. No. 4,291,701, issued Sept. 29, 1981 to the common assignee, for pressure transducing and methods and apparatus for building a cavity, and assigned to the subject assignee. In that copending application, I disclose, for example, a single-port pressure transducer dome in which a liquid injection needle is partially inserted into a straight passage of the port and is stopped by engagement inside the port short of the liquid-receiving cavity, while an overflow and gas escape path is provided through the straight passage along the outside of the stopped, partially inserted needle. If desired, the teachings of the subject invention may also be applied to those and other single-port dome structures.